Integrated process combining hydrofining and steam cracking

ABSTRACT

An integrated process for hydroconverting and steam cracking hydrocarbons is disclosed, comprising hydroconverting (particularly hydrodesulfurizing) a hydrocarbon to produce a hydroconverted hydrocarbon and heat; generating steam, using as part of the energy required the heat produced in the hydroconversion step; and contacting the hydroconverted hydrocarbon and the steam in a steam-cracking zone to form lowsulfur-content products. Alternatively, or in conjunction with the heat from the hydroconversion step, the heat produced in hydroconverting a lighter hydrocarbon fraction can be used in producing the steam.

United States Patent [1 1 Gould INTEGRATED PROCESS COMBINING HYDROFINING AND STEAM CRACKING Dec. 17, 1974 3,551,106 12/1970 Smith et a1 423/656 Primary Examiner-Delbert E. 631112 Assistant ExaminerS. Berger Attorney, Agent, or FirmG. F. Magdeburger; R. H. Davies; J. J. De Young 5 7] ABSTRACT An integrated process for hydroconverting and steam cracking hydrocarbons is disclosed, comprising hydroconverting (particularly hydrodesulfurizing) a hydrocarbon to produce a hydroconverted hydrocarbon and heat; generating steam, using as part of the energy required the heat produced in the hydroconver'sion step; and contacting the hydroconverted hydrocarbon and' the steam in a steam-cracking zone to form low-sulfurcontent products. Alternatively, or in conjunction with the heat from the hydroconversion step, the heat produced in hydroconverting a lighter hydrocarbon fraction can be used in producing the steam.

1 C1aim,1 Drawing Figure 2 72 oz E9 m; HYDROCRACKING E ZONE 11.1 ,5 I8 2 26 1- l8 Z (a 9 24 3 A 8 Z] 8 5 as STEAM I IHYDROFINING KING ZONE CRAC' Z Y ZONE 9 27 76 l o 5:; 1 F .1 22 I6 3 U l (I STEAM u. '5, GENERATION Y I E 23 4 19 1a 2.: I!

10 LLIHH ZONE INTEGRATED PROCESS COMBINING HYDROFINING AND STEAM CRACKING BACKGROUND OF THE INVENTION 1. Field of the Invention Processing of heavy hydrocarbon oil, such as vacuum residuum, atmospheric residuum, and asphalt-type materials is of particular concern to refiners. Not only do these materials have high sulfur contents, which makes it difficult to meet fuel oil sulfur specifications, but the l products are of relatively low value, making the economics of processing extremely important.

The formation of pitch and tar, together with gas, light oil and heavy oil fractions, by contacting heavy hydrocarbon oils such as vacuum residua with superheated steam at high temperatures, is known. Two of the major factors in the feasibility of such a process are:

l) the economics of producing this high-temperature steam; and (2) the sulfur content level acceptable in the resultant products. This invention is directed to an integrated process for hydroconverting hydrocarbons and steam crack ing hydrocarbons, combining processing steps in a highly efficient, integrated manner.

2. Description of the Prior Art As stated above, the use of steam to produce pitch or tar by contacting hydrocarbons with steam at high temdriving a turbine by heat exchanging a hot stream from a hydroconversion zone with water.

SUMMARY OF THE INVENTION The invention is directed to the use of the heat generated in an exothermic hydroconversion process as part of the energy necessary for generating superheated steam for steam cracking of hydrocarbons. It is particularly directed to an integrated process whereby heavy hydrocarbon oil feedstock is first hydrofmed with the concomitant production of heat; the heat from the hydroconversion process step. e.g., hydrofining, is recovered at least in part and used as part of the energy necessary to generate superheated steam; and the superheated steam, together with the hydrofined hydrocarbon, is fed to a steam-cracking zone, wherein the hydrocarbon oil is cracked to form tar and pitch as well as cycle oil and lighter gases.

By the integrated process of the subject invention, efficient utilization of the heat generated in the exothermic hydrofining or hydroconversion steps can be madein producing the superheated steam required in the steam-cracking process step. Additionally, the products from the steam-cracking process zone have lower levels of sulfur, making them more valuable products and eliminating the need for additional process equipment to remove the sulfur.

BRIEF DESCRIPTION OF THE DRAWING The Drawing is a diagrammatic illustration of the apparatus and flow paths suitable for carrying out one embodiment of the process of the present invention. Operating Conditions in the Hydroconversion Zone(s) The term hydroconversion as used herein is meant to encompass both hydrocracking and hydrofining in 0 which there is a net consumption of hydrogen. Hydrofining is meant to encompass both hydrodesulfurization and hydrodenitrification. Primarily hydrodesulfurization is being carried out in the hydrofming process. However, when the feedstock contains significant quantities of nitrogen, hydrodenitrification also is effected. I

The hydroconversion process step(s) is carried out at conventional temperatures and pressures. A temperature of fromabout 500 to. 900F., preferably 650 to 850F., is used. A pressure of from about 500 to about 10,000 psig, preferably 500 to 3,000 psig is used, with a liquid hourly space velocity of from 0.2 to 10.0, preferably 2.0 to 5.0. The hydrogen supply rate (makeup and recycle hydrogen) to the hydroconversion zone is inthe range of from about 5.00 to about 20,000 standard cubic feet per barrel of hydrocarbon feed, preferably about 2,000 to about.5,000 standard cubic feet per barreloAs noted above, while hydrodesulfurization will generally be the primary concern in the hydrofining zone, hydrodenitrification may also be of importance, dependent upon the hydrocarbon feedstock. Hydroconversion Catalyst The catalyst employed in the hydroconversion Zone(s) is comprised of material having hydrogenationdehydrogenation activity, together with an active cracking component. Exemplary cracking components include silica-alumina, silica-magnesia, silica-aluminazirconia composites, acid-treated clays. crystalline aluminosilicate zeolitic molecular sieve such as zeolite A, faujasite, zeolite ,X and zeolite Y. Hydrogenationdehydrogenation components of the catalyst preferably comprise at least one hydrogenation component selected from Group VI metals and compounds of Group VI metals and at least one hydrogenation component.

selected from Group VIII metals and compounds-of Group VIII metals. Preferred combinations of hydrogenation components include nickel sulfide with molybdenum sulfide, cobalt sulfide with molybdenum sulfide,

cobalt with molybdenum, and nickel with tungsten.

When the hydroconversion process step is hydrocracking, noble-metal-containing catalysts may also be used.

The preferred hydrofining catalyst is comprised of a carrier of alumina together with hydrogenation components of Group VI and Group VIII metals and compounds thereof, in which discrete, substantially insolu- 3,493,517, both of which patents are incorporatedherein by reference.

Operating Conditions in the Steam-Cracking Zone The steam cracking of hydrocarbons is carried out at a temperature in the range of from about l,500 to about 3,000F., preferably l,600 to 2,700F., and under a pressure in the range of from 6 to 300 psi absolute, preferably 14.7 to about 150 psi absolute. The treating time is in the range of from about 0.001 to about 0.1 seconds or, preferably, 0.003 to 0.05 seconds. The hydrocarbons fed to the steam-cracking zone may be sent directly to the steam-cracking zone without any intermediate cooling. That is, if the hydrocarbon fed to the steam-cracking zone is first hydrofined, the product may be sent to the steam-cracking zone at a temperature in the range of from 400 to 700F. This reduces the heating load to preheat the feedstock to the steam-cracking zone and provides a more efficient process. The steam fed to the steam-cracking zone is superheated and will be at a temperature from l,500 to 4,500F. Process Operation Referring now to FIG. 1, which represents a preferred embodiment of the present invention, crude oil is fed via line 1 to atmospheric distillation column 2. Atmospheric residuum is removed by line 3, and sent to vacuum distillation column 4. The vacuum gas oil fraction is taken off via line 5, combinedwith a heavy atmospheric gas oil (line 6) and fed via line 8 to hydrofining zone 9. The vacuum residuum in vacuum distillation column 4 is fed via line 10 to residuum hydrofining zone 11. A light gas oil is removed from column 2 and fed via line 7 to hydrocracking zone 12.

The effluents from hydroconversion zones 9, l1 and 12 are passed through steam boilers l3, l4 and 15, respectively, wherein heat is removed from effluent streams 16, 17 and 18, respectively. Steam is generated from the water passed through steam boilers 13, 14 and 15 by lines 19, and 21, respectively. Lines 19, 20 and 21 pass the steam generated in boilers 13, 14 and 15 to superheated-steam generator 22. Superheated steam is then fed by line 23 to steam cracking zone 24. The effluent from hydrofining zone 11 is fed by line 17 to steam-cracking zone 24. The effluent from steamcracking zone 24 is fed byline 25 to fractionator 26, where pitch, gas oil and other products are separated.

While the drawing constitutes one preferred embodiment of the present invention, it is clear that various modifications can be made in the present invention without departing from the spirit thereof. For instance,-

the atmospheric gas oil need not be combined with the vacuum gas oil before feeding to hydrofining zone 9. Also, the gas oil obtained from fractionator 26 may be subjected to steam cracking to produce unsaturated hydrocarbons such as ethylene, propylene and butadiene, using superheated steam generated using as part of the energy required the heat from a hydroconversion zone. Further, as pointed out above, it may be .desirable to send the hydrofined hydrocarbons from hydroconversion zone 11 directly to the steam-cracking zone without intermediate cooling. The basic concept of the'subject invention is the use of the heat generated in any or all of hydroconversion zones 9, 11 and 12 for producing the superheated steam used in the steam-cracking ing equipment for preheating the feed to the steamzone. Therefore, the vacuum residuum need not be first hydrofined, if operating conditions warrant it. The basic concept of the subject invention simply requires that the heat generated in hydroconverting hydrocarbons be used as part of the energy needed to generate the superheated steam used in steam cracking hydrocarbons. Feedstocks to the Steam-Cracking Zone A wide range of feedstocks may be used in the steamcracking zone(s). These feedstocks normally have boiling points in the range of from 350 to l,000F.+. Particularly preferred feedstocks are vacuum residua and other heavy hydrocarbon feedstocks such as reduced topped crude oils, atmospheric residua, crude shale oils, coal tar distillates, and the like. Mixtures of crude.

oils and distillate fractions, as well as mixtures of petroleum crudes and crude shale oils, etc., are also satisfactory feedstocks. Feedstocks used preferably contain substantial quantities of materials boiling above 1,000F Lighter feedstocks, such as light gas oils, ethylene cracker bottom oil, and the like, may also be used.

It is preferred that the feedstock to the steamcracking zone be first hydrofined to reduce sulfur content. By prior hydrofining of the feedstock to the steam-cracking zone, reduced sulfur content in the product is. obtained with the concomitant increased value of the product. Additionally, by feeding the effluent from the hydrofining zone directly to the steamcracking zone without any intermediate cooling, as by passing it through a steam boiler, the need for processcracking zone can be eliminated.

It is apparent that many widely different embodi ments in this invention may be made without departing from the scope and spirit thereof; and, therefore, it is not intended to be limited except as indicated in the appended claims. I i

What is claimed is:

1. An integrated process comprising:

a. atmospheric distilling a crude oil to produce a heavy atmospheric'gas oil and anatmospheric residuum;

b. vacuumdistilling said atmospheric residuum to produce a vacuum residuum and a vacuum gas oil;

c. hydrofining said vacuum residuum in a first hydrofining zone to produce a hydrofined vacuum resid- -UCtS. 

1. AN INTEGRATED PROCESS COMPRISING: A. ATMOSPHERIC DISTILLING A CRUDE OIL TO PRODCE A HEAVY ATMOSPHERIC GAS OIL AND AN ATMOSPHERIC RESIDUUM; B. VACUUM DISTILLING SAID ATMOSPHERIC RESIDUUM TO PRODUCE A VACUUM RESIDUUM AND A VACUUM GAS OIL; C. HYDROFINING SAID VACUUM RESIDUUM IN A FIRST HYDROFINING ZONE TO PRODUCE A HYDROFINED VACUUM RESIDUUM; D. HYDROFINING SAID HEAVY ATMOSPHERIC GAS OIL AND SAID VACUUM GAS OIL IN A SECOND HYDROFINING ZONE TO PRODUCE A HYDROFINED OIL AND HEAT; E. RRECOVERING AT LEAST PART OF THE HEAT PRODUCED IN STEP (D); F. GENERATING SUPERHEATED STEAM, USING THE HEAT RECOVERED IN STEP (E) AS A PORTION OF THE ENERGY REQUIRED TO PRODUCE SAID SUPERHEATED STEAM; AND G. CONTACTING SAID HYDROFINED VACUUM RESIDUUM AND SAID SUPERHEATED STEAM IN A STEAM-CRACKING ZONE TO PRODUCE LOW SULFUR-CONTENT STEAM CRACKED PRODUCTS. 